On a pc200lc-3 s/n 21277 how can you tell if engine speed sensor is bad? I have put manual gauges on it.
maybe you can use Digital Multi tester
Disconnect the electrical coupler at the sensor. Check both wires with an ohm meter. They usually fail by shorting through so there will not be any resistance. If it is good there will be something like 6 to something like 15 ohms. What I have seen the most is the rear main seal on the engine leaks and fills the damper case full of oil. The case gets hot and ruins the sensor. Make sure you drain the case if you change the sensor. It only holds about a pint and a half. You would think they would give you a code when they fail but unless there is high resistance the computer still thinks the thing is working. Good Luck!
Pull the sensor out and check for damage or any metal stuck to it as this can cause problems with bad readings.